1. Field of the Invention
The present invention relates to an endoscope including a bending portion in an insertion portion and, more particularly, to an endoscope in which an end portion of covering rubber forming an outermost circumference of the bending portion is fixed to a rigid portion near the end portion by bonding.
2. Description of the Related Art
As an endoscope for medical use inserted into a body, there are a rigid endoscope in which an insertion portion does not have flexibility and a flexible endoscope in which an insertion portion has flexibility. In recent year, not only the flexible endoscope but also some rigid endoscopes include a bending portion in an insertion portion.
As shown in FIG. 1, an insertion portion 1 of a flexible endoscope is configured by consecutively connecting a flexible tube portion 2, a bending portion 3, and a distal end portion 4 including a distal end rigid portion 4a in order. The flexible tube portion 2 is elongated and has flexibility. The bending portion 3 is configured to bend, for example, in upward, downward, left, and right directions.
The bending portion 3 includes plural bending pieces 5, a net tube 6 that covers an outer circumference of the plural bending pieces 5, and covering rubber 7 that further covers an outer circumference of the net tube 6. The plural bending pieces 5 are pivotably consecutively connected. The covering rubber 7 is an outer skin tube that covers the net tube 6.
A not-shown image pickup apparatus included in an observation optical system 8 is provided at the distal end portion 4 of the insertion portion 1. In the insertion portion 1, a signal cable extending from an image pickup device provided in the image pickup apparatus, a not-shown light guide fiber bundle for transmitting illumination light, a channel tube for suction 9, a bending wire 3a used to perform bending operation of the bending portion 3, and the like are inserted.
Japanese Patent Application Laid-Open Publication No. 2002-34900 discloses that, for example, a distal end bending portion and a flexible tube portion of an insertion portion of an endoscope is usually covered with an outer skin tube having flexibility, an end portion of the outer skin tube needs to be fixed to a tubular member on an inner side to prevent liquid from intruding from the outside, it is difficult to obtain a sure fixed state simply by bonding the end portion of the outer skin tube to the tubular member on the inner side using an adhesive, or, in the past, a method of tightly binding the end portion of the outer skin tube with a silk thread or a nylon thread to firmly fix the end portion of the outer skin to the tubular member on the inner side and further applying the adhesive from an outer side to prevent loosening of the thread is adopted.
In the insertion portion 1 of the endoscope shown in FIG. 1, a thread reeling and bonding portion 11 for firmly fixing a distal end portion of the covering rubber 7 to the distal end rigid portion 4a and a thread reeling and bonding portion 11 for firmly fixing a proximal end portion of the covering rubber 7 to a coupling member 10 are provided. These thread reeling and bonding portions 11 include thread members 12 and adhesives 13. The thread members 12 tightly bind the covering rubber 7 to the distal end rigid portion 4a and tightly bind the covering rubber 7 to the coupling member 10. The adhesives 13 are applied around the tightly-bound thread members 12.
However, in the insertion portion 1 of the endoscope, bending action of the bending portion 3 pulls the covering rubber 7 as indicated by an arrow Y2 in FIG. 2 and thickness of the insertion portion 1 decreases. When the bending action of the bending portion 3 is released, the pulled covering rubber 7 returns to an original state as indicated by a broken line.
In an endoscope for medical use, in recent years, high-temperature high-pressure steam sterilization has been adopted for disinfecting of the endoscope. When the endoscope is subjected to the high-temperature high-pressure steam sterilization, a waterproofing cap with a pressure regulating valve for adjusting pressure in a space on an inside of the endoscope is attached to an electric connector section of the endoscope. An endoscope including the same pressure regulating valve in a vent hole of a connector section of the endoscope is subjected to the high-temperature high-pressure steam sterilization without the waterproofing cap being attached to the endoscope.
Sterilization treatment by high-temperature high-pressure steam for the endoscope is performed in the order of a pre-process, a sterilization process, and a drying process. In the pre-process, pressure in a sterilization room is reduced and pressure on an outside of the endoscope is lower than an inside of the endoscope. Then, the pressure regulating valve of the waterproofing cap opens to allow the inside and the outside of the endoscope to communicate with each other. As a result, for example, a deficiency due to expansion caused by a large pressure difference between inner pressure of the endoscope and pressure in the sterilization room is prevented. In the pre-process, decompression is repeatedly performed at a predetermined time interval. Therefore, during the decompression, the covering rubber 7 expands, although a little. When the decompression is released, the covering rubber 7 is pulled to an inner side of the endoscope.
In the sterilization process, an inside of the sterilization room is pressurized, whereby pressure on the outside of the endoscope is higher than pressure on the inside of the endoscope. At this point, the pressure regulating valve is closed. The covering rubber 7 is pressurized as indicated by an arrow Y3 in FIG. 3 to thereby be crushed as indicated by a solid line from the state indicated by the broken line.
Thereafter, in the drying process, decompression is repeated as in the pre-process. As a result, the covering rubber 7 repeats deformation.
In this way, the covering rubber 7 is deformed in the bending action or in the high-temperature high-pressure steam sterilization. When the covering rubber 7 is deformed, a load is applied to an interface between the covering rubber 7 and the adhesive 13. It is likely that an end portion 13A of the adhesive 13, which fixes the covering rubber 7, peels as shown in FIG. 4.
As representative high-temperature high-pressure steam sterilization treatment, there is, for example, United States Standard ANSI/AAMI ST-79 issued by the Medical Equipment Development Association approved by the United States Standard Association. As specific conditions, it is specified that the treatment is performed for four minutes at 132° C. in the sterilization process including the pre-process.